A backhaul portion of a communication network is the intermediate links between a core network and access points of the communication network. Backhaul paths are e.g. used to connect radio base stations to a base station controller and to connect a large company's site to a metro Ethernet network. A backhaul path may be a wireless link, a wireline link or a combined wireless and wireline link. Accordingly different backhaul technologies may be used such as e.g. transmission technologies over optical fiber or copper cable, terrestrial or satellite point-to-point microwave radio relay transmission, different Digital Subscriber Line (DSL) technologies, Synchronous Digital Hierarchy (SDH) or Synchronous optical networking (SONET), or Ethernet.
There is a continuous development of new generations of mobile communications technologies to cope with increasing requirements of higher data rates, improved efficiency and lower costs. 3GPP Long Term Evolution (LTE) is a project within the 3rd Generation Partnership Project (3GPP) to improve the Universal Mobile Telecommunications System (UMTS) standard. The Universal Terrestrial Radio Access Network (UTRAN) is the radio access network of a UMTS and Evolved UTRAN (E-UTRAN) is the radio access network of an LTE system. In an E-UTRAN, a user equipment (UE) is wirelessly connected to a radio base station (RBS) commonly referred to as an evolved NodeB (eNB). A radio base station is a general term for a radio network node capable of transmitting radio signals. A radio base station may e.g. be a macro base station, a micro base station, a home eNodeB, a beaconing device, or a relay.
A majority of LTE base stations (i.e. eNBs) are expected to be deployed on legacy sites, which were originally designed for older types of radio base stations. The backhaul for these sites are typically designed for High Speed Packet Access (HSPA) data rates or lower and therefore cannot support the full traffic of a LTE base station. Therefore operators are replacing the existing backhaul with connections with significantly higher capacity. Due to its cost, this replacement will be made gradually so that some sites will have high data-rate backhauls while others will still have low data-rate backhauls.
Current standardization efforts within 3GPP for LTE-Advanced (LTE-A) will provide an alternative solution to using e.g. a cable or a micro-wave link as backhaul medium. The alternative solution is to allow an eNB in LTE-A to backhaul its data through another eNB, by using the same technology and the same frequency band as the access links. The new interface is called Un.
Backhauling that is achieved by using the same technology and the same frequency band as the access links will herein be referred to as in-band backhauling. Self-backhauling is another term that is sometimes used synonymously with the term in-band backhauling as defined herein. Analogously the term out-of-band backhauling will be used herein to refer to backhauling that uses a different technology and/or frequency band than the access links of the communications network. Similarly the term in-band interface will be used herein to refer to an interface that uses the same technology and frequency band as is used for access in the communications network and the term out-of-band interface will be used to refer to an interface that uses a different technology and/or frequency band than is used for access purposes.
The idea of in-band backhauling is to connect eNBs that do not have any out-of band backhaul to other eNBs that do have an out-of band backhaul.
In some cases an access point may have access to a plurality of alternate backhauls, such that the access point might change backhaul if there is a problem with a currently used backhaul.
The U.S. patent application US2007/0030809 A1 discloses a method comprising detecting a decrease in throughput over a current backhaul, determining whether there is an alternate backhaul available, and accessing the alternate backhaul.
Throughput is defined by the Internet Engineering Task Force (IETF) document RFC1242 as the maximum frame rate at which none of the offered frames are dropped by the device being measured. By extension, throughput along a network path is the maximum transfer rate at which no frames are dropped along the path. In practice, it has been observed that throughput values that could be measured along a network path depend on the protocol stack employed. As such, throughput measurements are specific to a given application and involve performing repeated experiments in order to determine the maximum transfer rate where no loss is observed. Such process is expensive in terms of network resource usage and potentially time consuming.
The available capacity on an IP link is defined in the IETF document RFC5136 as the link capacity multiplied by the complement of link utilization. In contrast with throughput measurements, there is a body of prior work that describes how to measure the available capacity on an IP link using methods which are less invasive than throughput measurements. Tools such as IGI, Yaz, pathChirp and BART (bandwidth available in real-time) are a few examples in this respect.
Manual backhaul configuration of a network may be a tedious and costly operation. Furthermore the fact that backhaul capacity may change in time and these capacity changes are independent on when the eNB are deployed and configured for the first time, may render manual backhaul configuration difficult. In addition, a network may have a very large number of eNBs. Therefore it is desired that backhauling may be automatically reconfigured.
The international patent application WO2007/106652A2 describes a controller that can dynamically select from a plurality of backhaul sites with which an access point can communicate via wireless backhaul channels. The controller can also generate a control signal that indicates to the access point to beam steer a backhaul signal to a certain backhaul site. The selection of backhaul site is based on information about the bandwidth capability of the backhaul site, e.g. if the backhaul site has a fiber optic connection, a T-1 connection or an ISDN or cable connection to a network node.
The known prior-art methods using throughput measurements does not necessarily yield a good estimate of the end-to-end available capacity for backhauling of an eNB, because of the underlying resource allocation and reservation techniques at the eNB. Furthermore many of the above mentioned prior art methods are not specifically adapted to a scenario in which a base station can select between an out-of-band backhaul and an in-band backhaul.
There is therefore a demand for improved methods and devices for backhaul selection and backhaul support that can provide good estimates of end-to-end available capacity for backhauling in a manner that is time efficient and efficient in terms of network resource usage.